The present invention relates to mine roof expansion anchors, and more specifically to novel bail elements for retaining tapered plug and shell portions in assembled relation prior to installation, and to anchors incorporating such bail elements.
Among the most common means of supporting the roofs and stabilizing and reinforcing rock strata in underground mines is an elongated rod having a threaded end anchored firmly in a drill hole in the rock formation by a mechanical expansion anchor. Such anchors include a radially expansible shell, a tapered nut or camming plug having a threaded bore for engagement with the threaded end of the rod and, in some cases, a strap or bail element for maintaining the shell and plug in assembled relation prior to installation. The shell may be of unitary design, having a plurality of leaves or fingers extending integrally from an annular base portion, or may include two or more physically separate portions connected via the bail.
The prior art includes many examples of expansion anchor bail structures which, in most cases, comprise a medial portion positioned over the larger diameter end of the plug and a pair of legs extending integrally from the medial portion to terminal ends permanently attached or otherwise secured with respect to the shell. Bails are usually fabricated from elongated strips of somewhat springy sheet metal having a width and thickness adequate to provide the necessary degree of rigidity. Examples of prior art bail structures may be found in U.S. Pat. Nos. 4,483,645, 4,516,886, 4,556,344 and 5,219,248 among others.
Among the requirements of a satisfactory bail element is the retention of the plug in predetermined relation to the shell and, after the anchor is engaged with the bolt and inserted in the drill hole, in a desired relation to the bolt and walls of the hole. Also, since expansion anchors are often installed in combination with a resin grouting material, it is desirable that the bail include structure or configuration which facilitates breaking the cartridge in which the components of the grouting mix are normally packaged.
The principal object of the present invention to provide a bail element of novel and improved configuration for retaining plug and shell portions of a mine roof expansion anchor in predetermined, assembled relation prior to installation.
Another object is to provide a mine roof expansion anchor having a bail element of novel configuration with enhanced capability of breaking the covering of a two-compartment resin cartridge which is inserted in the drill hole ahead of the anchor.
A further object is to provide a mine roof expansion anchor consisting of shell, plug and bail portions wherein the configuration of bail serves to maintain the shell and plug in a desired, assembled relation, and to assist in breaking a resin cartridge installed with the anchor, both in a novel and improved manner.